A photosensitive composition can be applied onto a substrate to form a coating film, the whole coating film is subjected to light exposure to form an insulating film or protective film, or a specific portion of the coating film is subjected to exposure by light irradiation using a photomask and then a non-exposure portion is subjected to a development treatment to remove it, thereby forming a pattern. This photosensitive composition have been used for photocurable inks, photosensitive printing plates, various photoresists, color filter photoresists for LCDs, photoresists for resin black matrixes, transparent photosensitive materials and the like since the photosensitive composition can be polymerized and cured by light irradiation.
Among photosensitive compositions, a transparent photosensitive composition is used in column spacers, overcoats and passivation films and usually contains an alkali-soluble resin binder, a polymerizable compound having an ethylenically unsaturated bond, a photopolymerization initiator and a solvent, but is not used in combination with a coloring aid such as a pigment.
A colored photosensitive composition is used in color filter photoresists and photoresists for resin black matrixes and usually contains red, green, blue and black colorants, an alkali-soluble resin binder, a polymerizable compound having an ethylenically unsaturated bond, a photopolymerization initiator and a solvent
In order to meet the demand for high quality and diversification of LCD applications, LCDs have been fabricated as applications for liquid crystal display device such as televisions and monitors, in addition to applications for conventional laptop and mobiles etc. For the purpose of improvement in productivity and durability, materials having high light-sensitivity and excellent mechanical properties have been demanded. When patterns are formed by photolithography or insulating protective films are formed by the whole exposure, high light-sensitive property, that is, photosensitivity is a factor playing a very important role. Further, for preventing the liquid display device from being broken by external impact and exhibiting its inherent performance, column spacers having a function as a support, and overcoats and passivation films having a function as protective films have to have excellent mechanical properties. Therefore, when a photopolymerization initiator having excellent photosensitivity is used, the above problems can be rapidly and preferably solved. When the photopolymerization initiator having excellent photosensitivity is used, it is advantageous in that sufficient sensitivity can be realized even when using a small amount of the photopolymerization initiator, and therefore it is possible to reduce the pollution sources of liquid crystal, improve the retention rate of the pattern and increase the usable amount of other raw materials in the production of a composition.
Further, in the case of a colored photosensitive composition, an extremely fine dispersion of the pigment has been carried out for the improvement in contrast or transmittance. In the case of a black matrix, high optical density (OD) values are required for improving the illuminance of backlight and hence the content of a black colorant is increased in the photosensitive composition. When the concentration of the colorant is increased, the amount of light transmitted to the lower portion of a film is suddenly decreased and thus through cure is lowered and the problem such as the delamination of a pattern and insufficient line width is occurred. Further, since the extremely fine dispersion of the pigment results in the expansion of the surface area thereof in the photosensitive composition and the amount of the photopolymerization initiator adsorbed onto the surface of the pigment is increased, there is a problem that an excess of the photopolymerization initiator is used for exhibiting sufficient sensitivity.
In order to solve these problems, the use of a photopolymerization initiator having excellent sensitivity is strongly demanded. In particular, if sufficient sensitivity is realized even when using a small amount of the photopolymerization initiator, it is possible to reduce the pollution sources of liquid crystal, improve the retention rate of the pattern and increase the usable amount of other raw materials in the production of a composition.
The known various types of photopolymerization initiators used in these photosensitive compositions include acetophenone derivatives, benzophenone derivatives, biimidazole derivatives, acylphosphine oxide derivatives, triazine derivatives and oxime derivatives.
Among them, the most typical commercially available photopolymerization initiators are acetophenone derivatives. The acetophenone derivatives have good color property and solubility, and are relatively inexpensive. In particular, since Irgacure 369 and Irgacure 907 available from Ciba Specialty Chemicals have excellent sensitivity, they are widely used in the applications of the colored photosensitive composition. However, since they should be used in an amount of 3% or more, even 10% or more of the solid content to exhibit sufficient sensitivity, they may tend to lower the retention rate and may be a cause of the pollution of liquid crystal. Further, a composition having a high concentration of a pigment, particularly since a black photosensitive composition has low sensitivity, severe delamination of a pattern occurs in the case of using it alone.
As other commercially available photopolymerization initiators, halomethyl triazine compounds that are decomposed by light irradiation to generate halogen radicals are frequently used. Particularly, the sensitivities of 2-aryl-4,6-bis(trihalomethyl)-s-triazine are known to be relatively excellent.
For example, JP-A No. 53-133428 describes the use of a compound having a bicyclic or polycyclic aromatic group or heterocyclic aromatic group, as an aryl group at the 2-position thereof. Particularly preferably a naphthyl group, leads to good results. The triazine-based compound has unsatisfactory sensitivity in the practical applications and has disadvantages in that the stability with time of a photosensitive composition is lowered due to its use in large quantities or long-term light irradiation, as well as insufficient solubility into a polymerizable compound having ethylenically unsaturated bonds.
The oxime derivatives have advantages that are almost never in color, and have high permeability, high radical-generating efficiency by UV irradiation, and excellent stability and compatibility in the composition, and thus have been extensively studied.
WO 00/52530 and German Patent Application Laid-Open No. 199 28 742 A1 describe a photosensitive composition using oxime ether, oxime ester, and particularly oxime sulfonate as a photoinitiator.
WO 02/100903 A1 describes an oxime ester compound having a structure bonded with alkyl acyl ketone, diaryl ketone or ketocoumarin.
In addition to these compounds, U.S. Pat. No. 4,202,697 describes an etch resist having an oxime ester structure and U.S. Pat. No. 6,001,517 describes a positive photosensitive composition comprising an oxime ester structure as a photosensitive cure accelerator.
However, among the oxime derivative compounds used as above, the initially developed compounds have low photoinitiation efficiency and do not effective for UV-light absorption in the case of having good color properties. The oxime derivative compounds published since the latter half of the 1990s have very good improved photoinitiation efficiency, but do not sufficiently satisfy the processing time conditions that were recently tightened.
In recent years, the commercially available oxime ester photopolymerization initiators, Irgacure OXE 01 and Irgacure OXE 02 (available from Ciba Specialty Chemicals) have considerably improved sensitivities and thus are being focused as the applications of colored photosensitive composition. However, since these photopolymerization initiators are very expensive, they cannot be used so as to exhibit sufficient sensitivity in terms of economy, and storage stability of the photopolymerization initiator itself is lowered.
Therefore, it has been desired the development of a photopolymerization initiator that is capable of overcoming the disadvantages of the above-mentioned photopolymerization initiators, and effectively absorbing UV radiation even when using a small amount thereof, and has excellent sensitivity and excellent high temperature process characteristics.